Imaging system and method of determining a translation speed of a catheter

ABSTRACT

Disclosed are an imaging system ( 10 ) or an interventional tool, such as a catheter ( 20 ), having a first ultrasound transducer array ( 23 ) and a second ultrasound transducer array ( 21 ) spaced by a fixed distance (D) from each other; wherein both arrays may be used to generate diagnostic images; and a processing arrangement ( 31, 32 ) to process a first sensor signal indicative of the first array imaging a reference location (X) at a first point in time, and to process a second sensor signal indicative of the second array imaging the reference location at a second point in time; and determine a translation (pullback) speed of the catheter from the set distance and the difference between the first point in time and the second point in time. Alternatively, a catheter may be provided comprising an ultrasound transducer array at a distal end of the catheter, and two pressure sensors for determining the translation speed.

This application is the U.S. National Phase application under 35 U.S.C.§ 371 of International Application No. PCT/EP2016/079364 filed on Dec.1, 2016, which claims the benefit of EP Application Serial No.15199715.2, filed Dec. 14, 2015. These applications are herebyincorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to an imaging system comprising aninterventional tool, such as catheter, a sensor arrangement on theinterventional tool for generating an in-vivo image and a processingarrangement communicatively coupled to the sensor arrangement.

The present invention further relates to a method of determining atranslation speed of the interventional tool, such as catheter, of suchan imaging system.

BACKGROUND OF THE INVENTION

Nowadays, catheter-based imaging systems find many applications inapplication domains where unaided visual inspection may be difficult orimpossible, e.g. cavity or drain inspections, and most notably, inmedical imaging where such imaging systems may be used to visualize theinternals of a patient, for example to detect an anatomical anomaly.

In certain applications, it may be important to be able to accuratelydetermine the size of an object imaged with the imaging system, e.g. incase of the object being a damaged or otherwise anomalous part of theimaged environment, as the size of the imaged anomaly may determine thesize of a repair object to be inserted into a channel carrying theanomaly. For example in medical applications, the imaging system may bean intravascular imaging system such as an intravascular ultrasound(IVUS) system used to image a coronary stenosis, in which case thelength of the coronary stenosis must be accurately determined in orderto determine the appropriate stent to be inserted into the coronaryartery to repair the coronary stenosis.

It is not straightforward to determine the size of such an anomaly fromthe images captured by the imaging system, e.g. due to the lack of(substantial) overlap between subsequently acquired images. Typically,this therefore requires knowledge of the translation, i.e. pull-back,speed of the catheter in order to appropriately scale the imagedanomaly. In order to have a well-defined pull-back speed, the pull-backof the catheter may be motorised. However, in certain applicationdomains such as medical applications, motorised pull-back of thecatheter is not preferred because of the overhead in terms ofconfiguration and handling involved with the operation of such animaging system. This for instance limits the number of investigationsthat can be performed per unit of time, e.g. per day, which may beundesirable.

US 2013/303914 A1 discloses an intravascular transducer delivery devicefor use with a patient. The delivery device comprises pressuretransducers adapted to measure both a pressure drop across a stenoticlesion and intravascular ultrasound transducers adapted to measure thesize of the vessel lumen adjacent the stenotic lesion. The respectivesensors are delivered to the site of the stenotic lesion with the samedelivery device. This solution is directed to determine the clinicalimpact of the stenotic lesion in order to determine the appropriatecourse of action (if any). However, it does not facilitate accuratedetermination of the size of the stenotic lesion such that where it isdecided that the insertion of the stent into the vascular regioncontaining the stenotic lesion is the appropriate course of action, thecorrect sizing of the stent cannot be derived from the sensorinformation provided by this delivery device.

SUMMARY OF THE INVENTION

The present invention seeks to provide an imaging system thatfacilitates accurate determination of the size of an anomaly imaged bythe imaging system in a mode of operation employing manual translation(pull-back) of its catheter.

The present invention further seeks to provide a method of determining atranslation speed of a catheter of such an imaging system.

According to an aspect, there is provided an imaging system comprising acatheter having a first reference object at a first location on thecatheter and a second reference object at a second location on thecatheter, the first location and second location being at a set distancefrom each other; a sensor arrangement including at least one sensor onthe catheter for generating an image with the catheter; and a processingarrangement communicatively coupled to the sensor arrangement andadapted to process a first sensor signal from the sensor arrangementindicative of the first reference object in a reference location at afirst point in time; process a second sensor signal from the sensorarrangement indicative of the second reference object in the referencelocation at a second point in time; and determine a translation speed ofthe catheter from the set distance and the difference between the firstpoint in time and the second point in time.

The provision of multiple reference objects on the catheter at setdistances from each other facilitates the determination of thetranslation speed of the catheter by the sensor arrangement generatingrespective sensor signals indicative of different reference objects at aparticular reference location at different points in time, such that thecatheter translation speed can be calculated from the time differencebetween different reference objects being at the same reference locationand the known distance between these reference objects. This facilitatesthe determination of the size of an anomaly, e.g. an anatomical anomaly,from the images captured by the sensor arrangement, e.g. from a sequenceof images imaging the anomaly.

The size of the anomaly may thus be determined by a user of the imagingsystem. Alternatively, the processor arrangement may be further adaptedto determine a size of an anatomical anomaly imaged with the sensorarrangement from the determined translation speed of the catheter; andgenerate an output indicative of the determined size of said anatomicalanomaly. This for instance may be achieved by the processor arrangementbeing adapted to recognize boundary features of the anomaly in the imageis provided by the sensor array, e.g. using well-known image processingalgorithms, and translate a time delay between receiving an imagecontaining the first boundary feature and receiving a further imagecontaining a second boundary feature opposite the first boundary featureinto a distance between such opposing boundary features using thedetermined translation speed of the catheter.

In a particularly advantageous embodiment, the at least one sensorcomprises an ultrasound transducer arrangement on the catheter forgenerating an in-vivo ultrasound image, which facilitates in-vivoimaging with minimal health risks for a patient. For example, theimaging system may be an IVUS imaging system.

In another particularly advantageous embodiment, the sensor arrangementcomprises a first sensor as the first reference object, the first sensoradapted to provide the processor arrangement with the first sensorsignal; and a second sensor as the second reference object, the secondsensor adapted to provide the processor arrangement with a second sensorsignal, wherein the processor arrangement is adapted to identify thereference location by matching the processed first sensor signal to theprocessed second sensor signal. In this embodiment, multiple referencesensors are positioned along the catheter at set distances from eachother to determine the translation speed of the catheter, which may besensors dedicated to provide reference data for determining the cathetertranslation speed or may be sensors having a dual purpose, e.g. toprovide imaging data as well as such reference data.

The first sensor may be arranged to generate a first plurality oftemporally discrete first sensor signals; the second sensor may bearranged to generate a second plurality of temporally discrete secondsensor signals; and the processor arrangement may be arranged to selecta second sensor signal from said second plurality for matching to afirst sensor signal from said first plurality based on a previouslydetermined translation speed of the catheter. Alternatively, theprocessor arrangement may be arranged to select a first sensor signalfrom said first plurality for matching to a second sensor signal fromsaid second plurality based on the previously determined translationspeed of the catheter. By predicting which of the sensor signals, e.g.images, in a stream of sensor signals is most likely to match apreviously sensor signal received from a downstream sensor, the amountof sensor signal processing required by the processor arrangement may bereduced as not all sensor signals of an upstream sensor need to beprocessed.

In an embodiment, the first sensor comprises a first ultrasoundtransducer array and the second sensor comprises a second ultrasoundtransducer array, and wherein the processor arrangement is adapted toidentify the reference location by generating a first ultrasound imagegenerated from the first sensor signal, generating a second ultrasoundimage generated from the second sensor signal and matching the firstultrasound image to the second ultrasound image. This image matching forinstance may be achieved by identification of the same distinct imagefeature, e.g. the same anatomical landmark, in the first ultrasoundimage and the second ultrasound image.

It may not be possible to exactly match images from different sensors toeach other, for example in scenarios where the orientation orpositioning of a downstream sensor relative to the reference location,e.g. a distinct image feature or anatomical landmark, has changedcompared to the orientation or positioning of the upstream sensorrelative to this reference location. For this reason, the processorarrangement may be adapted to match the first ultrasound image to thesecond ultrasound image by calculating a correlation between the firstultrasound image and the second ultrasound image; and determining thatthe first ultrasound image matches the second ultrasound image if thecalculated correlation exceeds a threshold value. In other words, whereit is determined that such images exhibit the highest (or high enough)degree of similarity, they are considered matching images.

In order to improve the likelihood of finding a match between differentimages from different sensors, the processor arrangement may be furtheradapted to perform at least one image adjustment operation on at leastone of the first ultrasound image and the second ultrasound image priorto matching the first ultrasound image to the second ultrasound image.Such image adjustment operations for example may be pre-processingoperations such as image centering, image intensity normalisation, imagerotation correction, and so on.

Alternatively, the first sensor and the second sensor are respectivepressure sensors, and wherein the processor arrangement is adapted toidentify the reference location by matching a pressure profile obtainedfrom the processed first sensor signal to a pressure profile obtainedfrom the processed second sensor signal. This for instance isparticularly advantageous in medical application domains such asintravascular imaging where vascular walls comprising anatomicalanomalies typically exhibit pressure profiles characteristic of theanomaly.

In a different embodiment, the sensor arrangement further comprises asensor external to the catheter adapted to generate the first sensorsignal and the second sensor signal, wherein the first reference objectis a first marker detectable by the sensor external to the catheter andthe second reference object is a second marker detectable by the sensorexternal to the catheter. Here, the reference location for example maybe a reference point of exit of the catheter from a body, e.g. apatient's body, into which the catheter has been inserted. By capturingexternal sensor signals, e.g. a sequence of images of part of thecatheter, in this reference location, the appearance of respectivereference objects a different point in time in these external sensorsignals is used to derive the translation (pull-back) speed of thecatheter from the body.

According to another aspect, there is provided a method of determining atranslation speed of a catheter of an imaging system, the cathetercomprising a first reference object at a first location on the catheterand a second reference object at a second location on the catheter, thefirst location and second location being at a set distance from eachother, the image system further comprising a sensor arrangementincluding at least one sensor on the catheter for generating an imagewith the catheter, the method comprising processing a first sensorsignal from the sensor arrangement indicative of the first referenceobject in a reference location at a first point in time; processing asecond sensor signal from the sensor arrangement indicative of thesecond reference object in the reference location at a second point intime; and determining the translation speed of the catheter from the setdistance and the difference between the first point in time and thesecond point in time.

This provides an accurate determination of the translation speed of thecatheter even in scenarios where the catheter is manually refracted(pulled back) from the body into which the catheter has been inserted.This for instance facilitates the calculation of the size of anomalysuch as an anatomical anomaly within a portion of the body imaged by thesensor arrangement on the catheter.

In an embodiment, the method further comprises generating a sequence ofimages indicative of the size of an anatomical anomaly with the sensorarrangement over a period of time; calculating the size of theanatomical anomaly from the period of time and the determinedtranslation speed of the catheter; and generating an indication of thecalculated size of the anatomical anomaly. Such automatic calculation ofthe size of the anatomical anomaly yields a particularly efficientoperation of the imaging system, thus minimizing the time required todetermine the size of the anatomical anomaly and maximising patientthroughput on the imaging system.

In an embodiment, the first sensor signal is a first image signal andthe second sensor signal is a second image signal, the method furthercomprising generating a first image generated from the first sensorsignal; generating a second image generated from the second sensorsignal; and matching the first image to the second image, for example byidentification (and superposition) of a distinct image feature in bothimages.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described in more detail and by way ofnon-limiting examples with reference to the accompanying drawings,wherein:

FIG. 1 schematically depicts an imaging system according to anembodiment;

FIG. 2 schematically depicts an imaging system according to anotherembodiment;

FIG. 3 schematically depicts an imaging system according to yet anotherembodiment;

FIG. 4 schematically depicts a flowchart of a method of determining acatheter pull-back speed according to an embodiment;

FIG. 5 schematically depicts a flowchart of a method of determining ananomaly size according to an embodiment; and

FIG. 6 schematically depicts an example embodiment of an imaging systemin more detail.

DETAILED DESCRIPTION OF THE EMBODIMENTS

It should be understood that the Figures are merely schematic and arenot drawn to scale. It should also be understood that the same referencenumerals are used throughout the Figures to indicate the same or similarparts.

The embodiments of the present invention are applicable to any type ofimaging system including a catheter for investigating a confined space.In particular advantageous embodiments, the imaging system is a medicalimaging system, such as an ultrasound diagnostic system. A particularlyadvantageous example of such an ultrasound diagnostic system is anintravascular ultrasound (IVUS) imaging system. In the remainder,embodiments of the imaging system will be described using an IVUSimaging system by way of non-limiting example only, as it should beunderstood that the described imaging system may be adapted fordifferent application domains without requiring inventive skill by aperson skilled in the art.

IVUS imaging procedures are widely used in interventional cardiology asa diagnostic tool for assessing a vessel, such as an artery, within thebody of the patient to determine the need for treatment, to guideintervention, and/or to assess the effectiveness of administeredtreatment. An IVUS imaging system uses ultrasound echoes to form across-sectional image of the vessel of interest. Typically, IVUS imaginguses a transducer in a catheter to emit ultrasound signals (waves) andto receive the reflected ultrasound signals. The emitted ultrasoundsignals (often referred to as ultrasound pulses) pass easily throughmost tissues and blood, but they are partially reflected bydiscontinuities arising from tissue structures (such as the variouslayers of the vessel wall), red blood cells, and other features ofinterest, e.g. a coronary stenosis.

FIG. 1 schematically depicts an IVUS imaging system 10 including acatheter 20 communicatively connected to a patient interface module 30through a communication structure 27, e.g. one or more conductive wires,which may form part of a larger structure such as a coaxial cable. Thecatheter 20 may be any suitable catheter, such as a solid-state catheteror a rotational catheter. An embodiment including a solid-state catheterwill now be described in more detail by way of non-limiting exampleonly.

The catheter 20 comprises an array 23 of transducers, here distributedaround a circumference of a sheath, which is an outer layer of thecatheter 20, e.g. near a distal end of the catheter 20 although itshould be understood that the array 23 of transducers may be positionedin any suitable location, e.g. at the distal end of the catheter 20. Thearray 23 of transducers may be formed in any suitable manner, e.g. byproviding a plurality of transducer chips on a flexible carrier tofacilitate the wrap-around of the array 23 around the sheath of thecatheter 20. Each chip may comprise one or more ultrasound transducers.Any suitable type of ultrasound transducers may be used for thispurpose, e.g. piezoelectric transducers, e.g. transducers formed ofpiezoelectric materials such as PZT and PVDF, or capacitivemicromachined ultrasound transducers (CMUT) in which a cavity separatesopposing electrodes, with a bottom electrode supported on a substrate ofthe CMUT cell and a top electrode supported by a flexible membrane, asis well-known per se. CMUT elements are particularly preferred due totheir lower cost and improved impedance characteristics compared topiezoelectric transducers.

The transducers are connected to an electronic multiplexer circuit (notshown), which may be located in the patient interface module 30, whichtypically comprises circuitry including one or more processing units,which will also be referred to as a processing arrangement. Themultiplexer circuit may form part of the processing arrangement or maybe a separate circuit in the patient interface module 30. Alternatively,at least part of the multiplexer circuit may be realized in circuitryembedded within the catheter 20. The multiplexer circuit is typicallyadapted to (sequentially) select transducers from the array 23 fortransmitting ultrasound signals and receiving reflected ultrasoundsignals. By stepping through a sequence of transmit-receive transducerpairs, the solid-state catheter 20 can be used to synthesize the effectof a mechanically scanned transducer element, but without moving parts.Since there is no rotating mechanical element, the transducer array 23can be placed in direct contact with blood and vessel tissue withminimal risk of vessel trauma.

The catheter 20 may comprise one or more lumens through which additionalstructures, e.g. a guide wire, may be fed as is well-known in the art.The catheter sheath may be made of any flexible material, e.g. anysuitable flexible polymer. Such materials are well-known per se and aretherefore not further elaborated upon for the sake of brevity only.

The catheter 20 further comprises a further array of transducers 21 at afixed distance D from the array of transducers 23. The further array oftransducers 21 preferably is identical to the array of transducers 23such that both transducer arrays can generate substantially identicalimages when located in substantially the same location, e.g.,substantially the same location relative to a reference point X when inuse. In the case of a medical imaging system 10, such a reference pointX for example may be a distinct image feature such as an anatomicallandmark within the part of the patient's body that is being imaged.Such a distinct image feature may be selected by a user of the imagingsystem 10, e.g. using a user interface (not shown) of the patientinterface module 30, e.g. by selecting the distinct image feature in animage displayed on the display device 33. Alternatively, such a distinctimage feature may be automatically selected by the processingarrangement, e.g. using one or more suitable feature recognitionalgorithms.

The further array 21 of transducers may act as a first sensor imaging areference point X at a point in time T1 during translation, i.e.pullback of the catheter 20 from a body, e.g. a patient's body, beingimaged with the imaging system 10. Such a first sensor may also bereferred to as a downstream sensor. The array 23 of transducers may actas a second sensor imaging the reference point X at a point in time T2during such translation of the catheter 20, with the array 23 producingsubstantially the same image of the reference point X as the array 21,but after a certain time delay ΔT=T2−T1. Such a second sensor may alsobe referred to as an upstream sensor. Consequently, the translationspeed S of the catheter 20 may be calculated as S=D/ΔT.

To this end, the processing arrangement of the patient monitoring unit30 comprises a signal processor 31 communicatively coupled to the array23 and the further array 21, which signal processor 31 is adapted toprocess the echo signals received from the respective arrays. The signalprocessor 22 may process the received echo signals in various ways, suchas bandpass filtering, decimation, I and Q component separation, andharmonic signal separation which acts to separate linear and nonlinearsignals so as to enable the identification of nonlinear (higherharmonics of the fundamental frequency) echo signals returned fromtissue and microbubbles. The signal processor 31 optionally may performadditional signal enhancement such as speckle reduction, signalcompounding, and noise elimination. The bandpass filter in the signalprocessor 31 may be a tracking filter, with its passband sliding from ahigher frequency band to a lower frequency band as echo signals arereceived from increasing depths, thereby rejecting the noise at higherfrequencies from greater depths where these frequencies are devoid ofanatomical information. Such signal processing techniques are well-knownper se and are therefore not explained in further detail for the sake ofbrevity only. Furthermore, it should be understood that additionalsignal processing techniques that are well-known per se to the personskilled in the art may be employed by the signal processor 31.

The signal processor 31 may further operate as an image processor or mayprovide the processed echo signals to a separate image processor 32forming part of the processing arrangement of the patient monitoringdevice 30. The image processor 32 is typically configured to determineif a first image produced from the echo signals of the first sensor,i.e. further transducer array 21, matches a second image produced fromthe echo signals of the second sensor, i.e. transducer array 23. To thisend, the image processor 32 may employ an algorithm using a metric basedon maximizing image correlation. For example, a correlation function mayuse an image correlation C, which may be defined as:

$C = \frac{\sum{I_{a,i}I_{b,i}}}{\sum{I_{a,i}^{2}{\sum I_{b,i}^{2}}}}$

In this equation, I_(a,i) and I_(b,i) are the intensities of the firstimage and the second image respectively. In order to calculate thecorrelation between the first and second image, the image processor 32may be further adapted to apply suitable image pre-processing stepsprior to calculating the correlation between these images. For example,the image processor 32 may employ image centering algorithms and/orimage intensity normalization algorithms in order to improve theaccuracy of the correlation calculation. In addition, the imageprocessor 32 may detect that the second image is rotated relative to thefirst image, e.g. due to a rotation of the catheter 20 during itstranslation, e.g. pullback. In such a scenario, the image processor 32may be adapted to compensate for such inter-image rotation. For example,suitable image rotation compensation algorithms include determination ofI(phi) by integration along the image radius, the use of 1-D correlationalgorithms to find the most likely angular offset, iteration estimationalgorithms of image position an angle, and so on. Such techniques arewell-known per se and are therefore not explained in further detail forthe sake of brevity only. Furthermore, it should be understood thatadditional signal processing techniques that are well-known per se tothe person skilled in the art may be employed by the image processor 32.The image processor 32 may apply a correlation threshold to determine ifthe first image matches the second image, i.e. may decide that such amatch exists if image correlation C exceeds a set threshold value. Tofurther improve the image matching process, the first image may becompared to a series of second images, e.g. consecutively capturedsecond images, with the second image having the largest (maximum)correlation with the first image being selected as the matching image,if its image correlation C also exceeds the threshold value. This is forexample preferable in scenarios where it is likely that multiple secondimages may ‘match’ the first image in terms of having an imagecorrelation C exceeding the set threshold value, in which case thesecond image having the best match, i.e. the maximum correlation, withthe first image may be selected to increase the accuracy of thedetermination of the translation speed of the catheter 20.

In order to determine the time delay or difference ΔT between matchingimages, the processing arrangement of the patient interface module 30,e.g. the signal processor 31 or the image processor 32, may employ aclock that provides each generated image with a timestamp.Alternatively, a separate clock may be used for this purpose. As suchtimestamping techniques are well-known per se, they will not beexplained in further detail for the sake of brevity only.

The image processor 32 may be adapted to, upon determination of areference location, e.g. an anatomical landmark, in an image produced bya downstream sensor, to evaluate every subsequent image produced by anupstream sensor until the best matching image produced by the upstreamsensor has been identified. However, where the respective transducerarrays produce images at high rates, it may be desirable to reduce thecomputational effort required by the image processor 32 in order tomatch these respective images. In an embodiment, the image processor 32is adapted to evaluate a subset of the images only produced by theupstream sensor, i.e. the transducer array 23, which subset is selectedbased on a previously determined translation speed of the catheter 20.For example, the image processor 32 may be adapted to only evaluateimages produced by the upstream sensor within a certain time windowW=[T_(a), T_(b)], with Ta=S*D*A and Tb=S*D*B, with A and B scalingfactors with A<1 and B>1, e.g. 0.5≤A<1 and 1<B≤1.5, such that areduction or an increase in translation speed of the catheter 20 up to50% is factored into the evaluation. Other suitable values of thescaling factors A and B will be immediately apparent to the skilledperson. It will be apparent to the skilled person that analogously theimage processor 32 may be adapted to evaluate a subset of imagesproduced by the downstream sensor within a certain time window to findthe best match with an image produced by the upstream sensor.

In an embodiment, the processing arrangement of the patient interfacemodule 30, e.g. the image processor 32, may be adapted to calculate thetranslation speed of the catheter 20, e.g. its pullback speed, from acomplete sequence of images captured with the respective transducerarrays 21, 23, which may be performed during or after acquisition ofthese images. In this embodiment, the processing arrangement may beadapted to apply regularization techniques such as a Kalman filter tothe image sequence in order to obtain a particularly accuratedetermination of the translation speed of the catheter 20.

Both the transducer array 23 and the further transducer array 21 may beused to generate diagnostic images, e.g. a composite image in which afirst portion of the image is generated by the transducer array 23 and asecond portion of the images generated by the further transducer array21. In the context of the present application, a diagnostic image may bean image used for a medical diagnosis of a particular condition withinthe body of a patient or may be an image for diagnosing a problem in anon-medical application domain as previously explained. Alternatively,one of the transducer arrays may solely be used for the purpose ofdetermining the translation speed of the catheter 20.

At this point, it is noted that the determination of the translationspeed of the catheter 20 is not limited to a transducer array 21displaced on the catheter 20 by a distance D relative to a transducerarray 23 on the catheter 20. Any type of sensor that is capable ofgenerating a sensor signal from which a reference point such as adistinct image feature or anatomical landmark can be recognized may beused for this purpose. For example, FIG. 2 schematically depicts anembodiment of the imaging system 10 in which the catheter 20 comprisesan ultrasound transducer array 25 at a distal end of the catheter 20,with the catheter 20 further comprising a first pressure sensor 21 at aset distance D from a second pressure sensor 23 on the catheter 20. Itis noted for the avoidance of doubt that the location of the firstpressure sensor 21, second pressure sensor 23 and ultrasound transducerarray 25 on the catheter 20 as shown in FIG. 2 is by way of non-limitingexamples only and that any suitable location for any of the sensors maybe contemplated, e.g. a location of the ultrasound transducer array 25in between the first and second pressure sensors or upstream from thefirst and second pressure sensors, i.e. closest to the proximal endportion of the catheter 20. Capacitive MEMS pressure sensors areparticularly preferred as this facilitates both CMUT image sensors andthe MEMS pressure sensors to be manufactured in the same manufacturingprocess. However, it should be understood that other suitable type ofpressure sensors, e.g. (piezo-resistive) strain gauges or Fabry-Perotpressure sensors, may be alternatively deployed.

In this embodiment, at least one of the first pressure sensor 21 and thesecond pressure sensor 23 may be included in the catheter 20 to providefurther diagnostic information to be processed by the processingarrangement of the patient interface module 30, e.g. to obtain pressureinformation from the wall of the blood vessel, e.g. an artery or vein,as is well-known per se. In an embodiment, both the first pressuresensor 21 and the second pressure sensor 23 are included in the catheterdesign to provide such diagnostic information. Such pressure sensorstypically generate pressure profile information, with the pressureprofiles may be compared with each other in analogy to the abovedescribed image comparison in order to match a first pressure profilegenerated by the first pressure sensor 21 to a second pressure profilegenerated by the second pressure sensor 23 after a time delay ΔT, suchthat the translation speed, e.g. the pullback speed, of the catheter 20,may be calculated from the known distance D between the first pressuresensor 21 and the second pressure sensor 23 and the determined timedelay ΔT.

In the above embodiments, the imaging system 10 comprises a pair ofsensors on the catheter 20 for capturing sensor data from which alandmark such as an anatomical landmark can be distinguished, e.g.distinct image features or pressure profiles. Such sensors may form partof the overall imaging functionality of the imaging system 10 or may besensors dedicated to the determination of the translation speed of thecatheter 20 as previously explained.

FIG. 3 schematically depicts an alternative embodiment in which thesensor arrangement of the imaging system 10 comprises an external sensor50 in addition to one or more sensors on the catheter 20. In thisembodiment, next to the sensor 25 for generating an image with thecatheter the catheter 20 comprises a first marker 41 detectable by theexternal sensor 50 and a second marker 43 detectable by the externalsensor 50 at a set distance D from the first marker 41. For example, theexternal sensor 50 may be an image sensor, which may be integrated in animaging device such as a camera. In this embodiment, the first marker 41and the second marker 43 may be visual markers that can be recognized inimages captured by the image sensor. Alternatively, the first marker 41and the second marker 43 may be inductive or magnetic markers detectableby an inductive or magnetic external sensor 50 respectively. Othersuitable detection principles may be contemplated.

During operation, the external sensor 50 is typically positioned withinsensor range of the catheter 20. For example, in the case of theexternal sensor 50 being an image sensor, the image sensor is typicallypositioned such that an image of the catheter 20 as it is being pulledback from a body (here symbolized by a human arm by way of non-limitingexample only) is captured by the image sensor such that the appearanceof such a visual marker emanating from the body being imaged can becaptured. In this embodiment, the body orifice through which thecatheter 20 is inserted into the body (or a fixed location in thevicinity of this body orifice) may be used as the reference locationused to determine the translation speed of the catheter 20, with theimage sensor typically set up to capture a sequence of images, e.g. atset intervals, of the reference location such that an appearance of oneof the visual markers in this reference location is captured in one ofthe images captured by the image sensor. As will be readily understoodby the skilled person, the same operating principle may be applied todifferent types of external sensors 50, e.g. magnetic or inductivesensors as previously explained. The time interval ΔT between theappearance of the first marker 41 in the reference location (as shown inthe left pane) and the appearance of the second marker 43 in thereference location (as shown in the right pane) may be determined byidentification of the respective markers in the sensor signals providedby the external sensor 50.

To this end, the external sensor 50 may be communicatively coupled tothe processing arrangement of the patient interface module 30, e.g. tothe signal processor 31 and/or to the image processor 32, with theprocessing arrangement adapted to analyze the sensor data provided bythe external sensor 50 (e.g. images in case of an image sensor), e.g.using feature recognition algorithms, which algorithms are well-knownper se and are therefore not described in further detail for the sake ofbrevity only, in order to identify a first sensor signal (e.g. image)identifying the first marker 41 and a second sensor signal identifyingthe second marker 43. The external sensor 50 may assign a timestamp toeach sensor signal sent to the patient interface module 30 oralternatively the processing arrangement may assign such a timestamp toeach sensor signal received from the external sensor 50 as previouslyexplained. The time delay ΔT may subsequently be calculated from thedifference in the respective timestamps of the sensor signals comprisingthe first marker 41 and the second marker 43 respectively in thereference location.

In case of the first marker 41 and the second marker 43 being visualmarkers, any suitable visual marker may be used as the first visualmarker 41 and the second visual marker 43. Preferably but notnecessarily, the first visual marker 41 and the second visual marker 43are identical markers, as this facilitates easy recognition of thesemarkers in the images provided by the image sensor 50. The visualmarkers may be an integral part of the catheter 20 or may be attachedthereto, e.g. as an adhesive tape or the like. The visual markers mayhave a contrasting colour to the colour of the catheter 20 to facilitatetheir recognition and/or may be a surface disruption such as anindentation or a ridge on the outer surface of the catheter 20, e.g. onits sheath. In case of a medical imaging system 10, the visual markersare biocompatible visual markers, i.e. visual markers that may beinserted into a patient's body without undue risk to the health andsafety of the patient.

The principle of the embodiment depicted in FIG. 3 can be alsoimplemented for an interventional tool tracking, such as catheter, withor without the sensor for generating an image. The sensor arrangement ofthe imaging system may be used for tracking the translation speed of theinterventional tool advancing in the body by means of the externalsensor 50 via processing the first sensor signal from the sensorarrangement indicative of the first reference object, such as marker 41,at the first location and the second reference object, such as marker43, at the second location.

It shall be understood that the principle of the present invention isapplicable not only to the catheters but to a broader class ofinterventional tools. In an aspect of the present invention theinterventional tool comprises the first reference object 21, 41 at afirst location on the tool and the second reference object 23, 43 at asecond location on the tool, the first location and second locationbeing at a set distance D from each other; a sensor arrangement 21, 23,25, 50 communicatively connectable to a processing arrangement 31, 32and comprising at least one sensor on the catheter for generating animage with said tool, wherein when the interventional tool is beingtranslated with a given translation speed the sensor arrangement isarranged to provide to the processing arrangement 31, 32 a first sensorsignal indicative of the first reference object in a reference locationX at a first point in time and a second sensor signal indicative of thesecond reference object in the reference location at a second point intime.

Yet another aspect of the present invention relates to the processingarrangement communicatively connectable to the sensor arrangement fromthe interventional tool and adapted to process the first sensor signalindicative of the first reference object in the reference location atthe first point in time; process the second sensor signal indicative ofthe second reference object in the reference location at the secondpoint in time; and determine the translation speed of the tool from theset distance and the difference between the first point in time and thesecond point in time.

The established means of the communicative connection between theinterventional tool 20 and the processing arrangement 31, 32 may be oneof wire-based and wireless.

In another aspect of the present invention a software implementedalgorithms is provided, said algorithm enabling a computer processor toperform functions of the processing arrangement 31,32 such as processthe first sensor signal from the sensor arrangement indicative;processing the second sensor signal from the sensor arrangement; anddetermining the translation speed of the interventional tool, such ascatheter, from the set distance and the difference between the firstpoint in time and the second point in time.

FIG. 4 schematically depicts a method to determine the translation speedof a catheter 20 using the imaging system 10 according to embodiments ofthe present invention. It shall be also understood that the describedbelow method can be used for a non-medical application such as cavity ordrain inspections, wherein precise measurements of the inspected cavityby a translatable tool (instead of the catheter compared to the medicalapplication) may be required. The method starts in 101, e.g. with theinsertion of the catheter 20 into a body, e.g. a patient's body, theimaging of the internals of the body, and the initiation of thepull-back of the catheter 20. In 103, first sensor data relating to afirst reference point on the catheter 20 being in the reference locationis captured. As previously explained, this may be sensor data generatedby a first sensor on the catheter 20, which sensor data includes adistinct image feature, e.g. a landmark such as an anatomical landmark,or may be sensor data provided by an external sensor capturing a firstdetectable marker appearing from the body. In 105, the sensor dataindicative of this reference location is processed by the processingarrangement of the imaging system 10, e.g. to identify the (anatomical)landmark or the detectable marker and to identify or assign a timestampto the sensor data.

In 107, second sensor data relating to a second reference point on thecatheter 20 being in the reference location is captured, e.g. sensordata generated by a second sensor on the catheter 20, which sensor dataalso includes the distinct image feature such as an (anatomical)landmark, or may be sensor data provided by an external sensor capturinga second detectable marker appearing from the body. The second sensordata subsequently is processed in 109, which processing may includepre-processing steps, such as for example in the case of the first andsecond sensor data relating to ultrasound images, where imagepreprocessing may be performed as explained above in order to facilitatethe determination of the correlation between these images.

In 111, the processed data is compared with each other to see if thedata is matching, that is, if both the first sensor data and the secondsensor data correlated to each other in the sense that both comprise a(pre-)defined distinct image feature such as a landmark or a detectablemarker in a defined location. If it is determined in 113 that no suchcorrelation exists, the second sensor data does not match the firstsensor data and the method reverts back to 107 in which new secondsensor data is captured. This is repeated until it is determined in 113that the first sensor data matches the second sensor data, after whichthe translation speed, e.g. the pullback speed, of the catheter 20 isdetermined in 115 from the known distance D between the first sensor 21and the second sensor 23 (or the first visual marker 41 and the secondvisual marker 43) and the time difference ΔT between the time of captureof the first sensor signals and the time of capture of the second sensorsignals as previously explained. It is reiterated that where referenceis made to the first sensor data matching the second sensor data in step113, this is intended to include finding the second image that has thelargest image correlation C with the first image. There may be more thanone second image that matches the first image in the sense that each ofsuch second images exhibit an image correlation C with the first imageabove a defined threshold (or vice versa), in which scenario the secondimage having the highest image correlation C may be selected as thematching image.

It is determined in 117 that the determination of the translation speedof the catheter 20 has been completed, the method terminates in 119,else the method may revert back to 103 to perform another determinationof the translation speed.

FIG. 5 is a flow chart of a method of determining the size of an anomalyimaged by the imaging system 10 using the catheter translation speed asdetermined with the method of FIG. 4. The method starts in 121 with theinsertion of the catheter 20 into a body to be imaged, after which in123 a sequence of images is captured of the internals of the body, whichsequence of images shows an imaged object or anomaly, e.g. an anatomicalanomaly such as a coronary stenosis in case of the imaging system 10being an IVUS imaging system. Although such a sequence of images istypically captured at a known capture rate, e.g. a known frame rate, itis nevertheless difficult to directly determine the size of the anomalyfrom the sequence of images due to the fact that neighboring images inthis sequence typically are non-overlapping, e.g. when capturing 2Dslices perpendicular to the translation direction of the catheter 20,with the spacing between subsequent 2D slices being unknown if thetranslation speed of the catheter 20 is unknown. Therefore, for the sizeof the anomaly to be accurately determined, the spacing betweenneighboring images has to be determined to be able to determine the rateof progress of the catheter 20 (e.g. the pullback speed of the catheter20), which often is unfeasible due to the lack of overlap (i.e. sharedanatomical landmarks) in these images.

In 125, the captured images may be processed, e.g. on the patientinterface module 30, which processing may include the determination of afirst anomaly boundary at point in time T=T_(a) in 127 and thedetermination of a second anomaly boundary at point in time T=T_(b) in129, with the size of the anomaly typically being defined by thedistance between the first anomaly boundary and the second anomalyboundary. However, as explained above, based on this sequence of imagesalone it is difficult to determine the size of the anomaly due to theunknown spacing between subsequent images in the sequence. Therefore, inaccordance with embodiments of the present invention, the size of theanomaly is estimated based on the translation speed S of the catheter 20as determined in accordance with the method as per the flowchart of FIG.4. Specifically, in 131, the size of the anomaly SA may be determined bythe formula SA=S*(T_(b)−T_(a)), i.e. by multiplication of the determinedcatheter translation speed S with the time delay between the image inwhich the first anomaly boundary and the image in which the secondanomaly boundary is captured. In 131, an indication of the size of theanomaly SA may be generated, e.g. a display control signal forcontrolling the display device 33 to display the calculated anomalysize.

In this manner, the size of a repair object for repairing the anomalywithin the body can be directly determined because the translation speedof the catheter 20 can be accurately determined without requiringwell-controlled translation, e.g. pullback, of the catheter 20, i.e.motorized pull-back.

It should be understood that the principles of the present invention maybe employed in any suitable type of imaging system including medicalimaging systems and non-medical imaging systems. As such systems arewell-known per se, a further description of such systems should not benecessary. Nevertheless, an example embodiment of an ultrasounddiagnostic imaging system 10 which may employ embodiments of the presentinvention is described in further detail with the aid of FIG. 6, whichschematically depicts a non-limiting example embodiment of such asystem.

In FIG. 6, an ultrasonic diagnostic imaging system 10 with a catheter 20according to an example embodiment of the present invention is shown inblock diagram form. In FIG. 6 a transducer array 25 is provided in acatheter 20 for transmitting ultrasonic waves and receiving echoinformation. The transducer array 25 may be a one- or a two-dimensionalarray of transducer elements capable of scanning in a 2D plane or inthree dimensions for 3D imaging. In some embodiments, the transducerarray 25 is a CMUT transducer array although other types of transducerarrays may also be contemplated. The transducer array 25 is coupled to amicrobeam former 22 in the catheter 20 which controls transmission andreception of signals by the array cells. Microbeam formers are capableof at least partial beam forming of the signals received by groups or“patches” of transducer elements for instance as described in U.S. Pat.No. 5,997,479 (Savord et al.), U.S. Pat. No. 6,013,032 (Savord), andU.S. Pat. No. 6,623,432 (Powers et al.)

The microbeam former 22 is coupled by the probe cable 27, e.g. coaxialwire, to a transmit/receive (T/R) switch 116 which switches betweentransmission and reception modes and protects the main beam former 120from high energy transmit signals when a microbeam former is not presentor used and the transducer array 25 is operated directly by the mainsystem beam former 120. The transmission of ultrasonic beams from thetransducer array 25 under control of the microbeam former 22 is directedby a transducer controller 118 coupled to the microbeam former by theT/R switch 116 and the main system beam former 120, which receives inputfrom the user's operation of the user interface or control panel 138.One of the functions controlled by the transducer controller 118 is thedirection in which beams are steered and focused. Beams may be steeredstraight ahead from (orthogonal to) the transducer array 25, or atdifferent angles for a wider field of view. The transducer controller118 may be coupled to control a voltage source 145 for the array 25. Forinstance, the voltage source 45 sets the DC and AC bias voltage(s) thatare applied to the cells of the array 25.

The partially beam-formed signals produced by the microbeam former 12are forwarded to the main beam former 120 where partially beam-formedsignals from individual patches of transducer elements are combined intoa fully beam-formed signal. For example, the main beam former 120 mayhave 128 channels, each of which receives a partially beam-formed signalfrom a patch of dozens or hundreds of transducer cells of the array 25.In this way the signals received by thousands of transducer elements ofa transducer array 25 can contribute efficiently to a single beam-formedsignal.

The beam-formed signals are coupled to a signal processor 31. The signalprocessor 31 can process the received echo signals in various ways, suchas bandpass filtering, decimation, I and Q component separation, andharmonic signal separation which acts to separate linear and nonlinearsignals so as to enable the identification of nonlinear (higherharmonics of the fundamental frequency) echo signals returned fromtissue and microbubbles.

The signal processor 31 optionally may perform additional signalenhancement such as speckle reduction, signal compounding, and noiseelimination. The bandpass filter in the signal processor 31 may be atracking filter, with its passband sliding from a higher frequency bandto a lower frequency band as echo signals are received from increasingdepths, thereby rejecting the noise at higher frequencies from greaterdepths where these frequencies are devoid of anatomical information.

The processed signals are coupled to a B-mode processor 126 andoptionally to a Doppler processor 128. The B-mode processor 126 employsdetection of an amplitude of the received ultrasound signal for theimaging of structures in the body such as the tissue of organs andvessels in the body. B-mode images of structure of the body may beformed in either the harmonic image mode or the fundamental image modeor a combination of both for instance as described in U.S. Pat. No.6,283,919 (Roundhill et al.) and U.S. Pat. No. 6,458,083 (Jago et al.)

The Doppler processor 128, if present, processes temporally distinctsignals from tissue movement and blood flow for the detection of themotion of substances, such as the flow of blood cells in the imagefield. The Doppler processor typically includes a wall filter withparameters which may be set to pass and/or reject echoes returned fromselected types of materials in the body. For instance, the wall filtercan be set to have a passband characteristic which passes signal ofrelatively low amplitude from higher velocity materials while rejectingrelatively strong signals from lower or zero velocity material.

This passband characteristic will pass signals from flowing blood whilerejecting signals from nearby stationary or slowing moving objects suchas the wall of the heart. An inverse characteristic would pass signalsfrom moving tissue of the heart while rejecting blood flow signals forwhat is referred to as tissue Doppler imaging, detecting and depictingthe motion of tissue. The Doppler processor receives and processes asequence of temporally discrete echo signals from different points in animage field, the sequence of echoes from a particular point referred toas an ensemble. An ensemble of echoes received in rapid succession overa relatively short interval can be used to estimate the Doppler shiftfrequency of flowing blood, with the correspondence of the Dopplerfrequency to velocity indicating the blood flow velocity. An ensemble ofechoes received over a longer period of time is used to estimate thevelocity of slower flowing blood or slowly moving tissue. The structuraland motion signals produced by the B-mode (and Doppler) processor(s) arecoupled to a scan converter 132 and a multiplanar reformatter 144. Thescan converter 132 arranges the echo signals in the spatial relationshipfrom which they were received in a desired image format. For instance,the scan converter may arrange the echo signal into a two dimensional(2D) sector-shaped format, or a pyramidal three dimensional (3D) image.

The scan converter can overlay a B-mode structural image with colorscorresponding to motion at points in the image field with theirDoppler-estimated velocities to produce a color Doppler image whichdepicts the motion of tissue and blood flow in the image field. Themultiplanar reformatter 144 will convert echoes which are received frompoints in a common plane in a volumetric region of the body into anultrasonic image of that plane, for instance as described in U.S. Pat.No. 6,443,896 (Detmer). A volume renderer 142 converts the echo signalsof a 3D data set into a projected 3D image as viewed from a givenreference point as described in U.S. Pat. No. 6,530,885 (Entrekin etal.).

The 2D or 3D images are coupled from the scan converter 132, multiplanarreformatter 144, and volume renderer 142 to an image processor 32 forfurther enhancement, buffering and temporary storage for display on animage display 40. In addition to being used for imaging, the blood flowvalues produced by the Doppler processor 128 and tissue structureinformation produced by the B-mode processor 126 are coupled to aquantification processor 34. The quantification processor producesmeasures of different flow conditions such as the volume rate of bloodflow as well as structural measurements such as the sizes of organs andgestational age. The quantification processor may receive input from theuser control panel 138, such as the point in the anatomy of an imagewhere a measurement is to be made.

Output data from the quantification processor is coupled to a graphicsprocessor 36 for the reproduction of measurement graphics and valueswith the image on the display 33. The graphics processor 36 can alsogenerate graphic overlays for display with the ultrasound images. Thesegraphic overlays can contain standard identifying information such aspatient name, date and time of the image, imaging parameters, and thelike. For these purposes the graphics processor receives input from theuser interface 138, such as patient name.

The user interface is also coupled to the transmit controller 118 tocontrol the generation of ultrasound signals from the transducer array25 and hence the images produced by the transducer array and theultrasound system. The user interface is also coupled to the multiplanarreformatter 144 for selection and control of the planes of multiplemultiplanar reformatted (MPR) images which may be used to performquantified measures in the image field of the MPR images.

As will be understood by the skilled person, the above embodiment of anultrasonic diagnostic imaging system is intended to give a non-limitingexample of such an ultrasonic diagnostic imaging system. The skilledperson will immediately realize that several variations in thearchitecture of the ultrasonic diagnostic imaging system are feasiblewithout departing from the teachings of the present invention. Forinstance, as also indicated in the above embodiment, the microbeamformer 22 and/or the Doppler processor 128 may be omitted, the catheter20 may not have 3D imaging capabilities and so on. Other variations willbe apparent to the skilled person.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims. In the claims, any reference signsplaced between parentheses shall not be construed as limiting the claim.The word “comprising” does not exclude the presence of elements or stepsother than those listed in a claim. The word “a” or “an” preceding anelement does not exclude the presence of a plurality of such elements.The invention can be implemented by means of hardware comprising severaldistinct elements. In the device claim enumerating several means,several of these means can be embodied by one and the same item ofhardware. The mere fact that certain measures are recited in mutuallydifferent dependent claims does not indicate that a combination of thesemeasures cannot be used to advantage.

The invention claimed is:
 1. An imaging system comprising: a catheter;an imaging arrangement on the catheter for generating an image with thecatheter; a sensor arrangement comprising a first sensor at a firstlocation on the catheter and a second sensor at a second location on thecatheter, the first location and second location being at a set distance(D) from each other; and a processing arrangement communicativelycoupled to the sensor arrangement and adapted to: process a first sensorsignal provided by the first sensor indicative of the first sensor in areference location (X) at a first point in time; process a second sensorsignal provided by the second sensor indicative of the second sensor inthe reference location at a second point in time; and determine atranslation speed (S) of the catheter from the set distance and thedifference between the first point in time and the second point in time;wherein the processing arrangement is adapted to identify the referencelocation by matching the processed first sensor signal to the processedsecond sensor signal; and wherein either: the first sensor and thesecond sensor are respective first and second ultrasound transducerarrays, the imaging arrangement comprises the first sensor and/or thesecond sensor, and the processing arrangement is adapted to identify thereference location by matching a first ultrasound image generated fromthe first sensor signal to a second ultrasound image generated from thesecond sensor signal; or: the first sensor and the second sensor arerespective first and second pressure sensors, the imaging arrangementcomprises an ultrasound transducer array, and the processing arrangementis adapted to identify the reference location by matching a pressureprofile obtained from the processed first sensor signal to a pressureprofile obtained from the processed second sensor signal.
 2. The imagingsystem of claim 1, wherein the processing arrangement is further adaptedto: determine a size of an anatomical anomaly imaged with the imagingarrangement based on the determined translation speed of the catheter;and generate an output indicative of the determined size of saidanatomical anomaly.
 3. The imaging system of claim 1, wherein the atleast one sensor on the catheter is configured for generating an in-vivoultrasound image.
 4. The imaging system of claim 1, wherein: the firstsensor is arranged to generate a first plurality of temporally discretefirst sensor signals; the second sensor is arranged to generate a secondplurality of temporally discrete second sensor signals; and theprocessor arrangement is arranged to select, based on a previouslydetermined translation speed of the catheter: a second sensor signalfrom said second plurality for matching to a first sensor signal fromsaid first plurality; or a first sensor signal from said first pluralityfor matching to a second sensor signal from said second plurality. 5.The imaging system of claim 1 when the first sensor and the secondsensor are respective first and second ultrasound transducer arrays,wherein the processing arrangement is adapted to match the firstultrasound image to the second ultrasound image by identification of asame image feature in the first ultrasound image and the secondultrasound image.
 6. The imaging system of claim 5, wherein theprocessing arrangement is adapted to match the first ultrasound image tothe second ultrasound image by: calculating a correlation (C) betweenthe first ultrasound image and the second ultrasound image; anddetermining that the first ultrasound image matches the secondultrasound image if the calculated correlation exceeds a thresholdvalue.
 7. The imaging system of claim 5, wherein the processingarrangement is further adapted to perform at least one image adjustmentoperation on at least one of the first ultrasound image and the secondultrasound image prior to matching the first ultrasound image to thesecond ultrasound image.
 8. A method of determining a translation speed(S) of a translatable tool of a medical imaging system, the medicalimaging system further comprising an imaging arrangement including atleast one sensor on the tool for generating an image with the tool asensor arrangement comprising a first sensor at a first location on thetool and a second sensor at a second location on the tool, the firstlocation and second location being at a set distance (D) from eachother, the method comprising: processing a first sensor signal providedby the first sensor indicative of the first sensor in a referencelocation at a first point in time; processing a second sensor signalprovided by the second sensor indicative of the second sensor in thereference location at a second point in time; and determining thetranslation speed of the tool from the set distance and the differencebetween the first point in time and the second point in time wherein themethod further comprises identifying the reference location by matchingthe processed first sensor signal to the processed second sensor signal;and wherein either: the first sensor and the second sensor arerespective first and second ultrasound transducer arrays, and theimaging arrangement comprises the first sensor and/or the second sensor,so that the identifying of the reference location is by matching a firstultrasound image generated from the first sensor signal to a secondultrasound image generated from the second sensor signal; or: the firstsensor and the second sensor are respective first and second pressuresensors, and the at least one sensor on the tool for generating an imagewith the tool comprises an ultrasound transducer array, so that theidentifying of the reference location is by matching a pressure profileobtained from the processed first sensor signal to a pressure profileobtained from the processed second sensor signal.
 9. The method of claim8, further comprising: generating a sequence of images indicative of asize of an imaged object with the imaging arrangement over a period oftime; calculating the size of the imaged object from the period of timeand the determined translation speed of the tool; and generating anindication of the calculated size of the imaged object.
 10. The methodof claim 8, wherein the reference point is an image feature.
 11. Themethod of claim 9 when the first sensor and the second sensor arerespective first and second ultrasound transducer arrays, whereinmatching the first ultrasound image to the second ultrasound imagecomprises identifying the same image feature in the first ultrasoundimage and the second ultrasound image.
 12. The method of claim 11,wherein matching the first ultrasound image to the second ultrasoundimage comprises: calculating a correlation (C) between the firstultrasound image and the second ultrasound image; and determining thatthe first ultrasound image matches the second ultrasound image if thecalculated correlation exceeds a threshold value.
 13. The method ofclaim 11, further comprising: performing at least one image adjustmentoperation on at least one of the first ultrasound image and the secondultrasound image prior to matching the first ultrasound image to thesecond ultrasound image.
 14. A medical imaging interventional toolcomprising: an imaging arrangement communicatively connectable to aprocessing arrangement and comprising at least one sensor on the toolfor generating an image; a sensor arrangement comprising a first sensorat a first location on the tool and a second sensor at a second locationon the tool, the first location and second location being at a setdistance (D) from each other, wherein, when the interventional tool isbeing translated with a translation speed (S), the first sensor isarranged to provide the processing arrangement with a first sensorsignal indicative of the first sensor in a reference location (X) at afirst point in time and the second sensor is arranged to provide theprocessing arrangement with a second sensor signal indicative of thesecond sensor in the reference location at a second point in time, sothat the processing arrangement can determine the translation speed (S)of the interventional tool from the set distance and the differencebetween the first point in time and the second point in time by matchingthe processed first sensor signal to the processed second sensor signalto identify the reference location; and wherein either the first sensorand the second sensor are respective first and second ultrasoundtransducer arrays, and the imaging arrangement comprises the firstsensor and/or the second sensor; or the first sensor and the secondsensor are respective first and second pressure sensors, and the atleast one sensor on the tool for generating an image comprises anultrasound transducer array.
 15. A processing arrangement fordetermining a translation speed (S) of a medical imaging interventionaltool of claim 14, the processing arrangement being communicativelyconnectable to the sensor arrangement of the medical imaginginterventional tool and adapted to: process a first sensor signalprovided by the first sensor of the sensor arrangement of the tool andindicative of the first sensor in a reference location (X) at a firstpoint in time; process a second sensor signal provided by the secondsensor of the sensor arrangement of the medical imaging interventionaltool and indicative of the second sensor in the reference location at asecond point in time; and determine the translation speed (S) of thetool from the set distance and the difference between the first point intime and the second point in time; wherein the processing arrangement isadapted to identify the reference location by matching the processedfirst sensor signal to the processed second sensor signal; and whereinthe processing arrangement is adapted to identify the reference locationby either: matching a first ultrasound image generated from the firstsensor signal to a second ultrasound image generated from the secondsensor signal, if the first sensor and the second sensor are respectivefirst and second ultrasound transducer arrays; or: matching a pressureprofile obtained from the processed first sensor signal to a pressureprofile obtained from the processed second sensor signal, if the firstsensor and the second sensor are respective first and second pressuresensors.